1. Field of the Invention
The present invention is related generally to a method for dry-cleaning garments or fabrics, and, more particularly, to such method, using liquid carbon dioxide as a solvent, alone, or along with surfactants or organic solvents, together with mechanical or sonic agitation in order to enhance the removal of insoluble/particulate soils.
2. Description of Related Art
A typical dry-to-dry-cleaning process consists of a wash, rinse, and drying cycle with solvent recovery. The garments are loaded into the cleaning drum and the cleaning fluid from a base tank is pumped into the drum to a predetermined level. During the wash and the rinse cycles, the drum tumbles the garments to provide the necessary agitation for soil removal. The solvent is then spun out of the drum and returned to the base tank through the appropriate filtration system. Some new machines use a closed loop system for solvent circulation during the wash cycle. The solvent is circulated continuously and at a high rate through the cleaning drum via a battery of filters. The high flow rates aid the rapid soil removal from the drum and result in lower soil re-deposition. At regular intervals, the cleaning fluid must undergo a distillation step to remove the dissolved soils and dyes. The stills are either part of the dry-cleaning machine itself, or self-standing.
Currently, the dry-cleaning industry uses perchloro-ethylene (PCE) (225 million pounds/year, 85% of establishments), petroleum-based or Stoddard solvents (55 million pounds/year, 12% of establishments), CFC-113 (11 million pounds/year, &lt;2% of establishments) and some 1,1,1-trichloroethane.
The dry-cleaning industry usually operates out of small, neighborhood-type shops. As such, the dry cleaners make up one of the largest groups of chemical users that come into direct contact with the general public.
All the solvents used present health risks, safety risks, and are environmentally detrimental: PCE is a suspected carcinogen, petroleum-based solvents are flammable and smog-producing, and CFC-113 is an ozone depletor and targeted to be phased out by the end of 1995.
Health risks due to exposure to cleaning solvents and the high costs of implementing and complying with safety and environmental restrictions and regulations have made dry-cleaning a much more difficult business in which to achieve profitability. For these reasons, the dry-cleaning industry is engaged in an ongoing search for alternative, safe, and environmentally "green" cleaning technologies, substitute solvents and methods to control exposure to dry-cleaning chemicals.
U.S. Pat. No. 5,267,455, as augmented by U.S. Pat. No. 5,279,615, discloses a dry-cleaning process for garments using both liquid and supercritical carbon dioxide as a cleaning medium, with or without the aid of cleanliness enhancing additives, along with a rotatable inner drum magnetically coupled to an electric motor.
Agitation of garments in a cleaning medium accelerates removal of soluble soils and is essential in the removal of particulate (insoluble) soils. However, the problems involved in fabricating a pressurized cleaning chamber with highly loaded internal moving parts, such as rotatable drum (as referenced above), and mainly the high costs associated with those problems, limit the commercial acceptability of such a process. This is particularly so for a neighborhood industry, such as dry-cleaning, where competition is high and profit margins are low to begin with.
Thus, there is a need for a method of dry-cleaning that employs health and environmentally-safe cleaning fluids at a competitive cost relative to the existing operations.